182 MOEPHOLOGY AND EVOLUTION
pectoralis quartus as it is in the Gorilla, and occasionally in the Siamang (181). In the Orang the claviciilar part is replaced by a slip from the rnanubrmm sterni and first costal cartilage; and the muscle is split into three parts.
The pectoralis minor varies considerably, as can be seen by a study of the writings of Bland-Sutton (402), Champneys (318), Humphry (340), Hepburn (83), Gratiolet (330), Wilder (414), Sonntag (399), Fick (247), Sornmer (491) and Kohlbriigge (199), In the Chimpanzee it arises from the first four, first five, second, third, and fourth, or third, fourth and fifth ribs; and it is inserted into the capsule of the shoulder-joint, the coracoid process, or both together, but the capsular insertion is most frequent. Sometimes it is double in the Chimpanzee as in the Gorilla, It arises in the Gorilla from ribs 3 to 7, in the Orang from the third and fourth ribs, and in the Gibbon from the third, fourth and fifth ribs. In the Gorilla and Orang it is inserted into the coracoid process; but it runs to the clavicle, coracoid process and conjoined tendons of the coraco-brachialis and biceps in the Gibbons.
The subclavins in the Chimpanzee and Gorilla is as in Man. In the Orang it rises from the first costal cartilage and second rib; but it springs from the second and third ribs in the Gibbon. It is enclosed between the layers of the costo-coracoid membrane.
The deltoid is coarsely fasciculate. In the Chimpanzee it arises from the front of the outer half of the clavicle, the outer border of the acromion, the whole length of the lower border of the spine of the scapula and the fascia over the infraspinatus. It covers a bursa